so been 2 months, all values are perfect and I do not do water changes
ammonia is zero
nitrate and nitrite are zero (DSP, nitrate sponge in filter)
Phosphate is under control and low

why perform a water change if everything is perfect ?
please tell me if there are anything I should watch out for
I also do top offs with tap water everyday._________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Well your tank is pretty new, given more time you will likely see a higher level of dissolved nutrients in your water resulting in a slow climb in nitrates, also a slow decrease in pH; and the tap water you are adding daily could also contain nitrates and phosphates (this is not uncommon with tap water) which often triggers an algae bloom; but this is not unusual in newer systems, so just keep an eye on it._________________Keepin' marines happy for 25 years

Waterchanges are also needed to dilute the hormones and such that animals release. If hormones get to "excessive" levels, it can impeded the growth and influence the health of organisms living in that environment._________________The Gymnogeophagus Study Group

What kind of testing are you using? Test strips are known to be very inaccurate, if you are using liquid tests then great! But remember, tanks can go down very quickly, also how big is your tank?_________________

What kind of testing are you using? Test strips are known to be very inaccurate, if you are using liquid tests then great! But remember, tanks can go down very quickly, also how big is your tank?

yea I'm using the liquid ones, its a 20G

I finally gave up and did a water change and added a skimmer,

turns out, with no water changes the success rate is pretty low. going to upgrade to a 65 G soon so need to find a way to at least minimize it

another thing was, I researched the elements that sea salt contains (about 70 of them) and in no way I can add all those 70 to the aquarium without a water change, Iodine, calcium, .... are just a couple which can be added but not other stuff_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral